Scandium is an important ingredient for specialty aluminum alloys for aerospace and other applications. In recent years, scandia (scandium oxide) has been shown to be highly beneficial as a stabilizer for zirconia (zirconium oxide) based solid oxide fuel cells for extending the service life and efficiency of these cells in generating electricity. With society's increasing emphasis on greener sources of energy, the use of solid oxide fuel cells is expected to grow substantially.
A restraining factor for the wider commercial use of scandium has been its limited availability, the lack of reliable long-term supply, and the very high cost of recovery.
Laterite ores, commercially processed for the recovery of nickel and cobalt, contain small (tens to hundreds of grams per metric tonne) quantities of scandium. The acid (usually sulfuric) leach processes used for nickel/cobalt recovery from these ores also extract the scandium into the leach solution to a significant (usually >90%) degree, see Haslam and Arnall, An investigation into the feasibility of extracting scandium from nickel laterite ores, In: ALTA 1999 and Cheng et 2011, Metallurgical processes for scandium recovery from various resources: A review, Hydrometallurgy, 108: 100-108, both of which are incorporated by reference in their entirety.
These processes, therefore, have the potential to become a significant new source for scandium, easing the supply constraints, and enabling wider application of scandium in meeting society's needs.
However, there are several challenges with the recovery of scandium from laterite acid each solutions. The scandium concentration in the leach solution is typically very low, generally <20 mg/L, and there are many other metals, besides Ni and Co, and other impurities, that are present in much higher, gram-per-liter, concentrations, which can interfere with the scandium recovery. The very low scandium concentration also means that its recovery directly from these solutions in commercially significant quantities will require treatment of very large volumes of solution.
In the prior art, methods are described in which scandium is recovered from laterite ore as a precipitate from the acid each solution after nickel and cobalt recovery as a sulfide precipitate (U.S. Pat. No. 5,756,056; Haslam and Arnall, An investigation into the feasibility of extracting scandium from nickel laterite ores, In: ALTA 1999) or from the pregnant leach solution (PLS) using solvent extraction (Pery et al., Scandium breathes new life into gold Greenvale nickel mine, In: ALTA 2012). However, these methods have the disadvantage of having to treat the entire volume of the leach solution, containing scandium at generally <20 mg/L levels, either before or after the nickel/cobalt recovery, while still having a number of impurities, such as iron, aluminum, silica, and others, at levels that are orders of magnitude higher than the scandium level—particularly if the scandium recovery is to be carried out before the nickel/cobalt recovery. This can make the scandium recovery operationally difficult and expensive.